Atom Pair Frequencies as a Quantitative Structure-Activity Relationship for Catalytic 2-Propanol Oxidation over Nanocrystalline Cobalt-Iron-Spinel

The purpose of this study is to find a direct and quantitative correlation of the structure of Co3-xFexO4 nanoparticles with catalytic performance in 2-propanol oxidation. Eight nanocrystalline samples with varying iron contents arc synthesized, and quantitative information regarding their structure is obtained from nitrogen physisorption, X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES), and extended X-ray absorption line structure (EXAFS) analyzed by reverse Monte Carlo simulations. The catalytic performance is tested in 2-propanol oxidation in the gas phase. Overall, catalytic conversion data as a function of temperature are deconvoluted to obtain conversion and half-conversion temperatures as quantitative parameters for the different catalytic reaction channels. The crystal structure is described by a spinel structure with interstitial cation defects. These defects result in a reduced electronic state of the nanoparticles. The defect density depends on the cationic composition. We also observe a complex cationic distribution on tetrahedral and octahedral sites, which is strongly influenced by the overall cationic composition. In the catalytic tests, the samples exhibit a low-temperature pathway, which is deactivated in subsequent runs but can be recovered by an oxidative treatment of the catalyst. We find that the frequency of cation pairs Co-O-Co-O and Co-O-Co-T of the individual samples correlates directly to their catalytic activity and selectivity.